A fourth generation (4G), for example, a long term evolution (LTE), communication method uses a packet-switched (PS) method and does not support a circuit-switched (CS) method. Accordingly, in order to provide a voice call function in an LTE terminal, a packet based voice communication, for example, voice over LTE (VoLTE), is used or a network (e.g., third generation (3G) network or second generation (2G) network) supporting a packet based voice communication is required.
For example, a terminal may provide both data service and voice service by using a radio frequency (RF) for LTE and an RF module for 2G/3G. In order to support such services, a communication technique such as simultaneous voice & LTE (SVLTE) or simultaneous global system for mobile communications (GSM) & LTE (SGLTE) may be applied to a terminal.
In relation to another method, a terminal may support voice/data services through one RF module by using a circuit switched fall back (CSFB) technique. For example, when there is an incoming call or a user makes a call, a terminal using an LTE communication network (e.g., a PS network) may connect a voice communication (and connect a data communication in 3G) as switching from an LTE network to a CS network in order for voice communication.
In general a CSFB method is a method for supporting voice communication when an LTE network does not support VoLTE. Moreover, when an LTE network supports VoLTE, a single radio voice call continuity (SRVCC) technique may be applied in order to hand over a voice call using VoLTE to a CS network (e.g., 2G/3G).
SRVCC, as may be inferred by the name, may maintain a voice call continuously by using single radio. If a terminal in a phone call using VoLTE moves to a place where no VoLTE is supported or the reception intensity of a signal is weaken, the terminal may perform cell searching for handover.
However, such cell searching takes a time for gap measurement procedure especially when single radio is used. For example, a terminal performs a measurement (e.g., GSM frequency) on a target cell during a current gap measurement time. Additionally, even if an LTE network becomes available after an SRVCC operation is completed or an LTE network becomes available during a call, a terminal may not maintain LTE service and, when a target cell does not support a multi radio access bearer, the terminal may not use data service during a voice call.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.